Certain portions of steam turbines, such as those employed in nuclear power plants, utilize pressure containment parts, made of ASME P-1 carbon steel. This material is not highly erosion resistant, but meets selected other engineering requirements. During the operation of steam turbines, the steam flow path through the turbine often causes unpredictable thermal-hydraulic characteristics, such as high velocity turbulent conditions, which result in an erosion-corrosion effect on these carbon steel parts. This erosion-corrosion reaction over time decreases the wall thickness of the pressure containing members and produces a rough surface. The rough surface, in turn, accelerates the effect of the erosion-corrosion reaction and further increases turbulence within the steam flow path.
To minimize erosion-corrosion damage in steam turbines, it has become necessary to provide a surface that exhibits resistance to the erosion-corrosion process. Since powder metallized surfaces are merely mechanically bonded and could result in eroded and detached pieces being pulled into the turbine, metallurgically bonded protecting alloys are preferred.
Typically, metallurgically bonded surfacing is applied with conventional arc welding methods with a variety of filler metals. However, conventional welding methods can lead to shrinkage stresses, excess heat input and thermal gradients within the base metal which often produce unacceptable distortion of the pressure containing parts. Such distortion can make it impossible to produce the required metal-to-metal steam containment necessary for turbine operation, therefore, additional grinding, machining, and/or temporary sealing compounds are generally required.
Accordingly, there is a need for a method of providing an erosion resistant surface to carbon steel steam turbine components which meets substantially all of the selected engineering requirements without causing appreciable deformation of the base metal during application. There is also a need to provide a metallurgically bonded erosion resistant surface to pressure containment parts which can withstand the harsh climate of erosion-corrosion effects. There is a further need for a surfacing operation which is capable of field application without the use of complicated positioning equipment.